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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 1. (January)

First Page: 146

Last Page: 146

Title: Depth-Gradient Analysis and Biotic Succession in Colony Creek Cycle (Late Pennsylvanian) of North Texas: ABSTRACT

Author(s): Noel L. Kennedy, Thomas E. Yancy

Article Type: Meeting abstract

Abstract:

The Colony Creek Shale (Canyon Group) in north Texas contains a vertical succession of lithologies and biotas deposited during regression from deep water to shallow water and strandline deposition. Stratigraphic successions in the Colorado River valley and the Brazos River valley of the outcrop belt are similar, showing that regression was of regional extent. A thin layer of platy, phosphatic black shale containing an ammonoid fauna occurs at the base of the Colony Creek and is diagnostic of deep-water deposition. This unit is similar to deposits of maximum transgression (stillstand) of many Pennsylvanian cycles. The overlying shoaling-upward portions of the Colony Creek are characterized by upward increase in sand content, increasing numbers and thicknesses of sand beds, and culmination in a horizon of subaerial exposure.

Statistical analysis reveals a continuum of communities in the shales of the Colony Creek. These communities represent the continuing response of organisms to shoaling but are partly the result of an increase in sand content within the shales. The basal phosphatic black shale contains a community distinguished by its ammonoids. The overlying gray shales contain a diverse pleurotomariid community, which grades upward into a Neospirifer-productid community. In shoal-water deposits a distinct Neospirifer-myalinid community appears. The top of the sequence contains a molluscan community in sand substrates, which is characterized by Permophorus. The brachiopod Crurithyris is dominant in most shales in the succession and is not depth controlled. This succession of lithologies and biotas is ypical of cyclothem deposits in other regions of North America and in Europe.

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